From a6778e9e7fb57603f15344ceb30098a3f6b7caf4 Mon Sep 17 00:00:00 2001 From: Ilija Hadzic Date: Mon, 31 Oct 2011 13:11:57 -0400 Subject: [PATCH] drm: add some comments to drm_wait_vblank and drm_queue_vblank_event during the review of the fix for locks problems in drm_wait_vblank, a couple of false concerns were raised about how the drm_vblank_get and drm_vblank_put are used in this function; it turned out that the code is correct and that it cannot be simplified add a few comments to explain non-obvious flows in the code, to prevent "false alarms" in the future v2: incorporate comments received from Daniel Vetter Signed-off-by: Ilija Hadzic Reviewed-by: Daniel Vetter Signed-off-by: Dave Airlie --- drivers/gpu/drm/drm_irq.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index cb3794a00f98..aa3ac0125d90 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1125,6 +1125,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe, trace_drm_vblank_event_delivered(current->pid, pipe, vblwait->request.sequence); } else { + /* drm_handle_vblank_events will call drm_vblank_put */ list_add_tail(&e->base.link, &dev->vblank_event_list); vblwait->reply.sequence = vblwait->request.sequence; } @@ -1205,8 +1206,12 @@ int drm_wait_vblank(struct drm_device *dev, void *data, goto done; } - if (flags & _DRM_VBLANK_EVENT) + if (flags & _DRM_VBLANK_EVENT) { + /* must hold on to the vblank ref until the event fires + * drm_vblank_put will be called asynchronously + */ return drm_queue_vblank_event(dev, crtc, vblwait, file_priv); + } if ((flags & _DRM_VBLANK_NEXTONMISS) && (seq - vblwait->request.sequence) <= (1<<23)) { -- 2.20.1